数据库中空记录怎么处理

[pcwak]

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
myconnection.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & Application.StartupPath & "\db.mdb"
mycommand.CommandText = "SELECT * FROM m 同学录 where 姓名='"& textbox1.text &"' "
mycommand.Connection = myconnection
myconnection.Close()
myconnection.Open()
Dim mysqlreader As OleDb.OleDbDataReader = mycommand.ExecuteReader
While mysqlreader.Read()
msgbxo("性别")
End While
End Sub
如果性别字段没有记录的话会出现错误，怎么办

[Latitude]

While mysqlreader.Read()
If not Convert.IsDBNull(mysqlreader("性别")) Then
msgbxo(mysqlreader("性别").tostring)
End if
End While

----
by Henry